The present invention relates to a silver halide photographic material, and more particularly to a silver halide photographic material containing a 2-equivalent naphthol-type cyan coupler.
In the subtractive color photographic process, as is well-known, a dye image is formed by the oxidiazation-coupling reaction effected inside silver halide emulsion layers between the oxidized product of an aromatic primary amine color developing agent produced when the developing agent reduces exposed silver halide grains and couplers which form yellow, cyan and magenta dyes. In the process, in general, open-chain active methylene group-having compounds are used as the yellow coupler for the formation of an yellow dye; pyrazolone-type, pyrazolotriazole-type, pyrazolinobenzimidazole-type, indazolone-type, and the like-type compounds are used as the magenta coupler for the formation of a magenta dye; and phenol-type and naphthol-type compounds are used as the cyan coupler for the formation of a cyan dye.
Those couplers which are unsubstituted at their reaction active sites are called four-equivalent couplers, which require stoichiometrically four-molar silver halide for the formation of a one-molar dye.
On the other hand, those couplers which are substituted at their reaction active sites by a group that can be split off without being affected by oxidation reaction are called two-equivalent couplers, which require only two-molar silver halide for the formation of a one-molar dye and therefore are useful for the economy of silver and which, because of being capable of improving the color-forming reaction speed, is known to have various other improving effects such as increasing the photographic speed, shortening the processing period of time through reducing the thickness of a silver halide photographic material, raising the image sharpness, and the like.
There are also known those various compounds produced by introducing into the reaction active sites of such couplers photographically useful groups (such as development inhibitors, development accelerators) or the precursors thereof, which release imagewise such photographically useful groups during the coupling reaction with the oxidized product of a developing agent.
Thus such two-equivalent couplers are intrinsically advantageous and are of wide application as compared to four-equivalent couplers, and therefore have a tendency to be frequently used lately.
Various attempts have been made with respect to making two-equivalent-type those naphthol-type cyan couplers conventionally used for the formation of cyan dyes.
For example, U.S. Pat. No. 3,227,554 describes those compounds having heterothio groups or arylthio groups as the substituent to the reaction active site. These compounds, however, although applicable to such a special use as of the inhibitor-releasing coupler, cannot be practically used as the image forming coupler due to their low dye-forming speed.
Those compounds formed by substituting couplers at their reaction active sites with a sulfonamido, acylamino, imido or the like group are also described in U.S. Pat. Nos. 3,737,316 and 3,458,315, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 25228/1975 and 21828/1976, and the like. However, they are still inadequate in the dye-forming speed and cannot make the most of the merit as the two-equivalent coupler.
Those most excellent as the reaction-active-site-substituent to two-equivalent couplers are alkyloxy groups and aryloxy groups, some of which groups are practically used. Typical examples of such groups are described in U.S. Pat. Nos. 3,476,563 and 3,822,248, Japanese Patent O.P.I. Publication Nos. 112038/1975, 18315/1977, 48237/1979, 32071/1980, 27147/1981, 12643/1981, and the like.
However, it is known that, even in these two-equivalent couplers, their dye forming reaction efficiency to the developing reaction of exposed silver halide grains is still low. The information media to combine these two reactions include the oxidized product of a color developing agent, but since the oxidized product is in itself unstable, it tends to lose its reaction activity prior to its coupling reaction with the coupler, and as a result the dye forming efficiency is considered to be lowered. The foregoing oxidized product of a color developing agent itself or a product changed therefrom is known to bleach the latent image of a silver halide and is considered also a cause of lowering the dye forming efficiency to the latent image. From the above facts it is understood that further increasing the reaction rate of such two-equivalent couplers enables the realization of higher photographic speed, economization of silver and more reduction of the layer thickness of photographic materials on a higher level.
It is also known that those naphthol-type two-equivalent cyan couplers produce more fog than do four-equivalent couplers and tend to cause a stain or fog trouble during the storage of raw photographic materials and to deteriorate the color formability, thus resulting in the deterioration of color reproducibility, which imposes restrictions on the designing of photographic materials.